The present invention relates to energy absorbing structures used in assemblies exposed to impact loads to control the amount of resulting damage to the assemblies and to protect the occupants or contents thereof. More particularly the invention relates to energy absorbing structures incorporated into motor vehicle frames to absorb impact energy and to a method of providing such structures.
The ever increasing number of road accidents has resulted in development of the present basic car body concept comprising a rigid cabin for occupants and deformable body parts having a high energy absorption capacity forwardly and rearwardly of the cabin. Aluminum and alloys thereof, due to excellent corrosion behavior, good extrudability, high ductility and low specific weight, consequently are natural material choices for motor vehicle body parts. However, the specific mass energy absorption of an aluminum extrusion construction having the same stiffness as steel sheet constructions, which have so far been used as energy absorbing structures in vehicles, can be twice as high as that of such steel sheet constructions. Such substantially higher specific energy absorption applied in the front part of vehicle would result in higher forces acting on vehicle occupants during a frontal collision. This means that in order to achieve a complete control of the energy absorption and the progressive collapse of the deformable body parts, ensuring a sufficient deceleration path so that the physical capacity of human bodies to survive a sudden stop is not exceeded, a simple switch over to application of, e.g., extruded Al-shapes in the energy absorbing structure is not possible.
Several approaches are known from the prior art to resolve this problem by e.g. provision of several individual sections having different material characteristics and being connected together by mechanical means or provision of reinforcing means attached outside or inside of the extruded shape at predetermined locations along an underdimensioned cross-section of the shape.
Apart from offering a rather complicated solution comprising several parts and the necessity of a laborious assembling operation, the provision of a reduced cross-section of the shape in the latter case also means reduced strength or stiffness of the structure overall, which is not desirable for the normal handling and performance of the vehicle frame.